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[PULL 17/26] target/arm: Make WFI a NOP for userspace emulators
From: |
Peter Maydell |
Subject: |
[PULL 17/26] target/arm: Make WFI a NOP for userspace emulators |
Date: |
Mon, 10 May 2021 13:25:39 +0100 |
The WFI insn is not system-mode only, though it doesn't usually make
a huge amount of sense for userspace code to execute it. Currently
if you try it in qemu-arm then the helper function will raise an
EXCP_HLT exception, which is not covered by the switch in cpu_loop()
and results in an abort:
qemu: unhandled CPU exception 0x10001 - aborting
R00=00000001 R01=408003e4 R02=408003ec R03=000102ec
R04=00010a28 R05=00010158 R06=00087460 R07=00010158
R08=00000000 R09=00000000 R10=00085b7c R11=408002a4
R12=408002b8 R13=408002a0 R14=0001057c R15=000102f8
PSR=60000010 -ZC- A usr32
qemu:handle_cpu_signal received signal outside vCPU context @ pc=0x7fcbfa4f0a12
Make the WFI helper function return immediately in the usermode
emulator. This turns WFI into a NOP, which is OK because:
* architecturally "WFI is a NOP" is a permitted implementation
* aarch64 Linux kernels use the SCTLR_EL1.nTWI bit to trap
userspace WFI and NOP it (though aarch32 kernels currently
just let WFI do whatever it would do)
We could in theory make the translate.c code special case user-mode
emulation and NOP the insn entirely rather than making the helper
do nothing, but because no real world code will be trying to
execute WFI we don't care about efficiency and the helper provides
a single place where we can make the change rather than having
to touch multiple places in translate.c and translate-a64.c.
Fixes: https://bugs.launchpad.net/qemu/+bug/1926759
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210430162212.825-1-peter.maydell@linaro.org
---
target/arm/op_helper.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/target/arm/op_helper.c b/target/arm/op_helper.c
index 78b831f1811..381f7857efb 100644
--- a/target/arm/op_helper.c
+++ b/target/arm/op_helper.c
@@ -285,6 +285,17 @@ static inline int check_wfx_trap(CPUARMState *env, bool
is_wfe)
void HELPER(wfi)(CPUARMState *env, uint32_t insn_len)
{
+#ifdef CONFIG_USER_ONLY
+ /*
+ * WFI in the user-mode emulator is technically permitted but not
+ * something any real-world code would do. AArch64 Linux kernels
+ * trap it via SCTRL_EL1.nTWI and make it an (expensive) NOP;
+ * AArch32 kernels don't trap it so it will delay a bit.
+ * For QEMU, make it NOP here, because trying to raise EXCP_HLT
+ * would trigger an abort.
+ */
+ return;
+#else
CPUState *cs = env_cpu(env);
int target_el = check_wfx_trap(env, false);
@@ -309,6 +320,7 @@ void HELPER(wfi)(CPUARMState *env, uint32_t insn_len)
cs->exception_index = EXCP_HLT;
cs->halted = 1;
cpu_loop_exit(cs);
+#endif
}
void HELPER(wfe)(CPUARMState *env)
--
2.20.1
- [PULL 08/26] target/arm: Move gen_aa32 functions to translate-a32.h, (continued)
- [PULL 08/26] target/arm: Move gen_aa32 functions to translate-a32.h, Peter Maydell, 2021/05/10
- [PULL 12/26] target/arm: Move vfp_reg_ptr() to translate-neon.c.inc, Peter Maydell, 2021/05/10
- [PULL 10/26] target/arm: Make functions used by translate-vfp global, Peter Maydell, 2021/05/10
- [PULL 09/26] target/arm: Move vfp_{load, store}_reg{32, 64} to translate-vfp.c.inc, Peter Maydell, 2021/05/10
- [PULL 11/26] target/arm: Make translate-vfp.c.inc its own compilation unit, Peter Maydell, 2021/05/10
- [PULL 14/26] target/arm: Move NeonGenThreeOpEnvFn typedef to translate.h, Peter Maydell, 2021/05/10
- [PULL 15/26] target/arm: Make functions used by translate-neon global, Peter Maydell, 2021/05/10
- [PULL 13/26] target/arm: Delete unused typedef, Peter Maydell, 2021/05/10
- [PULL 16/26] target/arm: Make translate-neon.c.inc its own compilation unit, Peter Maydell, 2021/05/10
- [PULL 18/26] hw/sd/omap_mmc: Use device_cold_reset() instead of device_legacy_reset(), Peter Maydell, 2021/05/10
- [PULL 17/26] target/arm: Make WFI a NOP for userspace emulators,
Peter Maydell <=
- [PULL 22/26] hw/arm/imx25_pdk: Fix error message for invalid RAM size, Peter Maydell, 2021/05/10
- [PULL 20/26] include/qemu/bswap.h: Handle being included outside extern "C" block, Peter Maydell, 2021/05/10
- [PULL 19/26] osdep: Make os-win32.h and os-posix.h handle 'extern "C"' themselves, Peter Maydell, 2021/05/10
- [PULL 21/26] include/disas/dis-asm.h: Handle being included outside 'extern "C"', Peter Maydell, 2021/05/10
- [PULL 23/26] hw/misc/mps2-scc: Add "QEMU interface" comment, Peter Maydell, 2021/05/10
- [PULL 25/26] hw/arm/mps2-tz: Implement AN524 memory remapping via machine property, Peter Maydell, 2021/05/10
- [PULL 24/26] hw/misc/mps2-scc: Support using CFG0 bit 0 for remapping, Peter Maydell, 2021/05/10
- [PULL 26/26] hw/arm/xlnx: Fix PHY address for xilinx-zynq-a9, Peter Maydell, 2021/05/10